In medicine there are many applications requiring the control of the flow of fluids such as, for instance, of biological fluids. One such application, for example, is the control of the blood flow during an extracorporeal blood treatment otherwise known as hemodialysis. During hemodialysis treatment, a patient's vascular system is connected to a hemodialysis machine for sessions that can last several hours. This connection forms a blood circuit, whereby blood is drawn from the patient through a needle connected to a flexible blood line, cycled through a hemodialysis machine that removes waste products including water, urea, and other impurities of the blood, and returned to the patient via a second blood line and needle.
In order to withdraw blood from a patient, a blood access is commonly created in the nature of an arterio-venous shunt, refereed to as a fistula. During the blood treatment, blood is taken out from the fistula at an upstream position of the fistula and is returned to the fistula at a downstream position.
Alternatively a polytetrafluoroethylene (PTFE) can be used to access a patient's bloodstream. A PTFE graft is an artificial blood vessel used to connect an artery to a vein. The material used for the graft is suitable for puncturing with needles to achieve the necessary access to the patient's blood system.
A third method of obtaining access to a patient's blood for hemodialysis is to use percutaneous catheters, which allow blood to be withdrawn from one lumen and returned by a second lumen. As can be appreciated there may be a number of other different ways to access a patient's blood for hemodialysis.
During the procedure of hemodialysis it is advantageous to operate with blood flows at the highest rates possible in order to maximize the efficiency of the treatment, while avoiding damage to the blood cells. One difficulty that can arise in chronic hemodialysis is maintaining adequate blood flow during treatment sessions. When flow rates decrease significantly, an attendant can sometimes restore adequate flow by switching the blood lines. In the past, the attendant would turn off the hemodialysis machine and physically switch the lines connecting the hemodialysis machine and patient. The line that was previously drawing blood from the patient and carrying it to the machine is switched such that it supplies blood from the machine to the patient. The other line that was previously supplying blood to the patient is then switched to draw blood from the patient. Once the lines are switched the hemodialysis machine is turned back on and the process continues.
There are several problems with physically switching the blood lines during hemodialysis. One problem is that the disconnecting and switching of lines is a time consuming process that further lengthens an unpleasant hemodialysis procedure for the patient. Another problem is that the switch may cause bleeding and allow air to enter the lines. Disconnecting the lines also breaks the microbe barrier, which increases the possibility of infection. Thus, blood lines are often not switched during hemodialysis treatment, unless it is absolutely necessary.
There have been some attempts to solve the problem associated with switching blood lines during hemodialysis. For example in U.S. Pat. No. 5,894,011 to Prosl et al., (the entire disclosure of which is hereby incorporated herein by this reference), relates to a device for selectively controlling the direction of blood flow to and from the patient during hemodialysis and comprises two interlocking disks that rotate in relation to each other without separating. The two disks have fluid fittings that allow the bloodlines attached to the patient to connect to one of the disks and the blood inlet and outlet for the hemodialysis machine to connect to the other. In the center of each fluid fitting is a channel that aligns to a corresponding channel in the other disk. The disks rotate between two fixed relative positions, referred to as preferred alignments. The preferred alignments are such that the line drawing blood from the patient in the first preferred alignment becomes the line returning blood to the patient in the second preferred alignment, and the line returning blood to the patient in the first preferred alignment becomes the line drawing blood from the patient in the second preferred alignment. Thus, blood flow between the two patient lines can be reversed without reversing flow through the two unit lines and the connected hemodialysis machine.
Problems common to the above devices having rotating bodies in direct contact with blood include, for example, a risk that the blood clots or clogs in the space between the two rotatably connected parts and that blood cells may be damaged during rotation of the rotatably connected parts. Many patients who are dependent on dialysis also have a low production of blood cells. Thus, it is important to avoid damaging blood cells during dialysis. Thus, multiple reversals of blood flow is not advisable using such devices having rotating bodies.
Another problem with devices having rotating bodies is the cost of producing such a device is significantly large considering such devices are one-time use devices because sterilization of such components is impractical. It is preferable to keep costs of preferred disposable devices to a minimum if they are to become commercially viable.
Also, PCT Patent Application No. WO2005/061043 to Gambro Lundia AB, (the entire disclosure of which is hereby incorporated herein by this reference), shows a further attempt to provide a solution for the switching of lines problem associated with hemodialysis. The switching device in the '043 application includes a deformable portion having four ports, two of which are connected to the patient and two of which are connected to the hemodialysis machine. The device operates in a first and second clamping position, where a wedge squeezes the deformable portion in different directions to change the flow of blood. One problem associated with the device in the '043 application is that the wedge used to interact with the deformable portion has a straight edge. The straight edge causes the blood to have a radical change of direction when it enters the switching device, which may damage the blood cells or cause blood clotting in the device.
The wedge set forth in the Gambro Lundia PCT application is designed to have a straight edge because of the configuration of the four ports of the device. Namely the four ports do not join at a single point but rather form a connection network that resembles a square. The square connection is divided into two when the wedge intersects the deformable portion. As noted above, the problem with this particular configuration is that the blood undergoes non-trivial stresses as it enters the switching mechanism, thus potentially exposing blood cells to undesired shear forces.
Furthermore potential blood stagnation occurs within the device in certain portions, such that there is risk for blood clotting to occur. Blood clots within any blood tubing is very worrisome because those clots could either go towards the patient, potentially leading to major problems, or less problematic to the dialysis machine, where it nevertheless can interfere with the quality of the dialysis treatment.